The present disclosure generally relates to an intramedullary nail for internal fixation of a bone, such as a femur. The disclosure further relates to an implant system for use in orthopaedic surgery and to a method of manufacturing an intramedullary nail.
Femur fractures commonly occur in the femoral neck and the trochanteric regions. Today, trochanteric and sub-trochanteric femur fractures are treated with an intramedullary nail having a transverse bore in a proximal portion to receive a femoral neck screw usually provided in the form of a lag screw. Such a nail is shown in U.S. Pat. Nos. 5,176,681 and 5,454,813, the disclosures of which are incorporated herein by reference.
For fracture treatment the intramedullary nail is, in a first step, fitted in the intramedullary canal of the femur. Then the lag screw is passed through the transverse bore of the intramedullary nail, through the neck of the femur and into the femoral head. When implemented, a connecting fastener is inserted through a bore in a distal portion of the intramedullary nail to fasten the intramedullary nail to bone.
The lag screw is designed to transfer the load from the femoral head into a shaft of the nail while bridging the fracture line to allow fast and secure fracture healing. Further, the lag screw is allowed to slide in the intramedullary nail in accordance with the sintering of the femoral fracture.
U.S. Pat. No. 7,763,022 B2 relates to an intramedullary nail having a transverse bore for receiving a femoral lag screw at the proximal portion. The transverse bore has at an inlet opening a notch in form of an outer rounded edge. The notch ensures reduction of stress peaks in the end portions of the bore when the femoral lag screw is loaded (e.g., by the force of the patient's weight), specifically at the inlet opening.
U.S. 201000174284 relates to an intramedullary nail with a proximal portion including a cutout positioned adjacent to a transverse bore on the lateral side of the intramedullary nail.
U.S. Pat. Nos. 7,527,627 and 7,780,667 relate to an implant system with an intramedullary nail having a proximal transverse bore formed by two overlapping circular holes, wherein the proximal circular hole is smaller in diameter than a distal circular hole. The resulting 8-shaped transverse bore receives a fastener assembly comprising a lag screw used in conjunction with a compression screw.
It has been found that non-unions of peri and intratrochanteric fractures as well as sub-trochanteric fractures treated with an intramedullary nail can lead to overloading and thus breakage of the implant. Specifically, conventional intramedullary nails may be damaged at their smallest cross sectional area of the proximal portion, i.e., in the area of the transverse bore, for example during drilling with a lag screw step drill. Such a damage may lead to a weakening of the intramedullary nail in a critical area and result in brakeage of the implant when it is overloaded, (e.g., by the patient's weight). Moreover, the stability between the intramedullary nail and the femoral lag screw is decreased in such a situation and the implant system may fail to hold the fracture in a stable configuration, such that a well-defined compressive sliding of the femoral lag screw can no longer be guaranteed.